Balloon catheters are used in procedures relating to the treatment of stenoses or blockages in body vessels, an example of which is an arterial stenosis which is commonly treated by angioplasty procedures which involve the insertion of balloon catheters into the affected blood vessel of the patient.
The balloon may function to widen a vessel into which the catheter is inserted, to force open a blocked vessel to open the blocked or collapsed blood vessel, or to prop open the collapsed vessel. The requirements for strength and size of the balloons vary widely depending on the balloon's intended use and the vessel size into which the catheter is inserted. Perhaps the most demanding applications for such balloons are in balloon angioplasty in which catheters are inserted for long distances into extremely small vessels and used to open stenoses of blood vessels by balloon inflation.
Balloon angioplasty requires extremely thin walled, high strength (i.e. high tensile), relatively inelastic balloons of predictable inflation properties.
Thin walls are necessary because the balloon's wall and waist thicknesses limit the minimum diameter of the distal end of the catheter and therefore determine the limits on vessel size treatable by the method and the ease of passage of the catheter through the vascular system. High strength is necessary because the balloon is used to push open a stenosis and so the thin wall must not burst under the high internal pressures necessary to accomplish this task. The balloon must have some elasticity so that the inflated diameter can be controlled, so as to allow the surgeon to vary the balloon's diameter as required to treat individual lesions, but that elasticity must be relatively low so that the diameter is easily controllable. Small variations in pressure must not cause wide variation in diameter.
To achieve the high strength, thin walled properties, catheter balloons are often made of biaxially oriented polyethylene terephthalate (PET) or a polyamide material such as nylon 12. These materials, however, tend to be less elastic, and have less resilience.
Balloon catheters may also be made of more elastic materials such as polyolefins or polyolefin copolymers, but typically, in order to achieve the high tensile strength, the balloon walls must be made thicker.
One difficulty experienced in the case of the high strength, thin walled materials, such as PET is that they can be punctured through abrasion or the like, even though they have a high tensile strength. Pin holes and ruptures can occur when such catheter balloons are used in contact with rough surfaces. Also, tiny flaws in the mold of such balloons can create weak spots, since the balloons are so thin-walled.
It is, however, typically impractical to increase the wall thickness of these biaxially oriented, non-resilient materials because they become too stiff, with high flexural moduli, with the result that such balloons do not collapse properly on deflation to facilitate easy withdrawal from the vascular system of a patient.
The balloons can be coated with a more abrasion resistant material, but coatings add a step during the manufacturing process, typically decrease flexibility, and also typically increase the wall thickness.
There remains a need for a balloon catheter which is thin walled, durable, abrasion and tear resistant thereby improving the resistance to pinhole formation, and is relatively flexible, yet inelastic to allow the balloons to expand outwardly to a predetermined diameter, and then cease further expansion at normal pressures, to avoid damage to the artery wall by overexpansion.